Speaking to French outlet Le Parisien, the 26-year-old could hardly contain his delight with his international teammates remarkable run of form this season.
The Real Madrid star said: "Seeing him do this moves me personally because I know how much he's been criticised and mocked.
“I've been his biggest supporter since we were 14. I've always said, even when he wasn't scoring, that he was one of the best players in the world. Some thought I was just saying that because I liked him. But I know the difference between friendship and reality on the pitch.
Dembele, 27, has struggled with injuries throughout his career but has finally found his feet under Luis Enrique at PSG.
Mbappe added: "Ousmane reached maturity at 27, which is normal in football. There are players who are more precocious, so some might have thought he was arriving late.
“But no, Ousmane Dembele has never arrived late; it's the normal evolution of a footballer, who reaches his full potential at 27. He still has great years ahead of him.
“I'm very happy for him and I hope he continues like this. He deserves what he's getting; he's worked hard for it."
The winger has scored an impressive 30 goals in his 37 games across all competitions this season, with 22 of those goals coming in 2025.